A few weeks ago this column dealt with atmospheric nuclear tests and their environmental and health impacts. However, since the Limited Test Ban Treaty of 1963, most explosive nuclear tests have been conducted underground. Nuclear establishments around the world have tried to convince their citizens and others that these tests posed no risks to their health and the environment. However, even the limited amount of data that is available suggests that this is not the case.
The initial environmental impacts of an underground nuclear explosion are associated with the seismic shock wave that results from the release of a tremendous amount of energy to the Earth surrounding the point of explosion, and the radioactive elements produced during the nuclear explosion, which in some cases may escape into the atmosphere. We consider these two in turn.
About 1% or less of the energy released in an underground nuclear explosion is transmitted as a seismic wave. This produces temporary ground motions just like an earthquake. As with naturally occurring earthquakes, ground motion from seismic waves arising from nuclear detonations could damage buildings and other structures. Nuclear testing in the Pacific has also caused damage to coral reefs with consequences to fish and other marine life.
For example, high rise buildings in Las Vegas more than 160 km away from the Nevada test site in the United States have been known to sway following underground nuclear explosions. In July 1979, a French nuclear test in the Mururoa Atoll led to an underwater landslide. This in turn created a tidal wave causing at least one technician to be seriously injured. It has been reported that following the Indian nuclear tests in May 1998, some houses in the nearby village of Khetolai had sustained some damage.
The nuclear reactions that are responsible for the energy produced in the explosion also leave behind radioactive remnants. In the first few minutes after a nuclear explosion, over 300 radioactive species are produced. Within an hour or so, this reduces to about 60 species since short-lived elements decay rapidly. At this time, the residues from a one-kilotonne explosion undergo approximately 1018 (a billion billions) radioactive disintegrations per second, equivalent to about 30 million Curies. Some of the key radioactive remnants from underground testing are Cesium-137, Strontium-90, Plutonium-239, Carbon-14, Tritium and Iodine-131.
As mentioned earlier, some of these radioactive residues do make their way to the atmosphere. This could be a result of �venting� (failure to contain the radioactivity due to faulty design), gradual seepage of radioactive gases into the atmosphere over a period of weeks or months, or �operational releases� whereby radioactivity was released during routine post-test activities.
With the exception of four �peaceful nuclear explosions�, all tests at the Nevada Test site in the United States following the Limited Test Ban Treaty (723 in all) were designed to completely contain the radioactivity underground. Nevertheless, about 55% of all tests led to radioactivity being released to the atmosphere. In the Soviet Union, nearly 60% of the underground nuclear tests conducted at the Novaya Zemlya test site released radioactivity into the atmosphere.
Most of these releases are typically small compared to releases from atmospheric tests and were largely localised. However, radioactive nuclides from 52 US nuclear tests were detected outside the test site (about 1300 square miles in area), often at dose rates several times the background radiation rate. Radioactivity from the 1970 Baneberry test was detected as far away as Canada.
The major environmental impacts of the two mechanisms discussed so far - seismic waves and atmospheric releases of radioactivity - are relatively short-lived. The long term health and environmental damage from underground testing would likely arise from the immense quantities of radioactive material, much of it hazardous for very long time periods, left below the ground. These could eventually contaminate ground water or even come to the surface.
For long, officials in charge of nuclear testing have claimed that because all the radioactive material is trapped within the cavity left behind by the explosion, this vast accumulation of radioactive material under the ground did not lead to any hazards. Recent studies have, however, demonstrated that radioactive materials do indeed escape from the cavity and migrate significant distances. For example, according to the 7 January 1999 issue of the international science magazine, Nature, scientists have detected plutonium 1.3 kilometres away from a 1968 nuclear weapons test in Nevada.
Predicting how humans would be exposed to these in the future is complex and uncertain. It would depend on factors like population densities, life styles and resource use. However, it may be said with certainty that exposure to these radioactive materials, as with radioactive exposures through other pathways, has deleterious health consequences.
Over the last few decades, epidemiological and microbiological research has increasingly revealed that exposure to even low levels of radiation is hazardous. There is no scientific evidence for any threshold below which radiation doses may be considered �safe�. Broadly speaking two kinds of effects are predominant - an increase in the incidence of cancers and mutations to genes. In addition, exposure of in utero foetuses to radiation could affect future physical and mental development of the unborn children.
To summarize, testing of nuclear weapons has led to and would continue to cause damage to human health and the environment. It is essential that the health of the potential victims of nuclear testing is monitored regularly and medical treatment provided. Test sites must be immediately closed down to stop further damage to health and the environment and opened up to independent agencies for environmental remediation.
